User Manual

MDR2400 and MDR5800 User Manual
862-01881 Issue 8 Page 24
3.5 Microcell Backhaul Applications of MDR Digital Radios
In applications where more than one independent and separate links, need to radiate from a
central site, a number of parameters can be taken advantage of, to provide isolation and minimise
interference between these links:
• Frequency multiplexing
• Antenna polarisation
• Choice of High Antenna Gain
It is important to note that these methods only provide isolation between two radio Systems, and
that power levels in the separate systems should be balanced to ensure correct operation.
3.5.1 Setting the Transmitted Power Levels
To minimise interference, received power levels should be balanced between separate radio links.
This means that transmit power levels should be set to provide similar levels of received power, as
indicated by the RSSI values of the adjacent receivers at the central site.
3.5.2 Frequency Multiplexing
The MDR2400 offers three frequency channel plans and the MDR5800 offers four frequency
channel plans. A radio link requires two channels (one for transmit and one to receive) to provide
full duplex operation. Each radio has a high and a low sub-band, one that it uses for transmission
and another for reception. Terminology definition: the ‘High-band Outdoor Unit’ of a system
transmits on the higher of the two sub-bands. The ‘Low-band Outdoor Unit’ of a system transmits
on the lower of the two sub-bands. A system (link) always has one High Band and one Low Band
Outdoor Unit. It is important to note that unwanted transmitted signals in adjacent frequency bands
can affect other receivers operating in an adjacent band if insufficient antenna isolation is
provided. A solution is to group high-band or low-band Outdoor Units at the central site, rather than
group high and low-band Outdoor Units together.
3.5.3 Antenna Isolation
Separate links at a central site will have sufficient isolation when radio systems operate outside
the radiation beamwidth or side lobes of the system antenna. The achievable isolation can be
established by examining the measured radiation patterns of the system antennas. Directional
isolation can be used if the antenna radiation is 15 dB or lower relative to the adjacent main beam.
Antennas with high directionality will allow reduced angular separation of adjacent systems.
Antenna cross-polarisation isolation can be used for adjacent radio links, radiating in the same
direction. Typical isolation of 30 dB can be achieved using high quality antennas.